This invention pertains to high voltage electrical devices, and in particular to insulating conductor supports for internal high voltage leads which pass through apertures in internal braces and the like frame-work members located within those devices. This invention finds particular application with respect to insulating conductor supports for high-voltage conductors which interconnect the coils of multi-phase power class transformers. Such conductors are relatively heavy, and require support so as to be held in a fixed location, thereby eliminating shifting of the conductors which may cause the insulation on such conductors to wear away in time, resulting in an unintentional grounding of those conductors. Conductors of the aforementioned type used in multi-phase transformers span generally vertical and horizontal distances, receiving support from wood or fiber braces which form part of an internal framework of the transformer. At points where the conductors pass through apertures formed in the braces, an insulating fiber collar enclosing the conductors is provided to enhance the dielectric strength of the insulation system extending between the conductors, the brace, and grounded portions of the transformer. These collars are typically secured to the brace by an adhesive, by a clamping arrangement, such as a split clamp, or by other fastening devices of inferior dielectric strength compared to the remaining insulation system. Such adhesives or clamping arrangements, when combined with the brace, impair the dielectric strength of that brace, thereby reducing the electrical insulation between the high voltage conductor and adjacent grounded portions of the device's internal framework.
In the past, manufacturers of large electrical devices were able to rely on large oil-filled spaces between high voltage conductors and grounded internal brace members. But now it is desirable to reduce the overall size of such equipment, thereby reducing the large oil-filled spaces, bringing high voltage conductors and grounded parts closer together, thereby increasing the electric field stresses to which the insulating parts are subjected during factory testing and operation. Consequently, energized parts must be insulated by members having a dielectric strength greater than that heretofor required. Also, the operating and testing voltages of such equipment are being increased, and high voltage electrical testing standards impose protracted over-voltages on such equipment, which further increases the stress which the internal insulating systems of such devices are called upon to withstand. Any corona discharge, and/or electrical tracking, caused by excessive electrical stresses within such devices must be avoided, since localized carbonization and gas formation due to decomposition of organic materials exposed to the discharges will be experienced. Carbon particles or gasses resulting from such localized discharges will become suspended in the dielectric fluids within which such devices are immersed and which are circulated throughout an electrical device to provide cooling to the internal portions thereof. Such carbon particles or gasses suspended in such circulated fluids may present a heightened possibility of dielectric failure throughout the electrical device, thereby reducing the reliability of the electrical device, and possibly the integrity of the power system within which the device is installed.
The presence of adhesives, metallic clamping arrangements or the like inferior dielectric apparatus located immediately adjacent high voltage conductors which pass through portions of internal framework, present a substantial risk that corona discharge will occur either during testing of the device, or during its subsequent operation. Such risk of corona discharge and possible insulation failure must be avoided since large electrical devices require a substantial capital investment and also, due to their physical size and complex electrical connection, are not readily replaceable. Further, these devices are expected to remain in continous service over 30 or more years of operation. Should excessive internal electrical discharge or insulation failure occur, the devices must be taken out of service, which usually inconveniences the consumers who are supplied electrical energy through the electrical devices.
An economic manufacture of such electrical devices requires that the insulating supports of internal electrical conductors be easily installed to surround one or more previously installed conductors without adhesives, or clamping arrangements.